Students and Robots
Last year Zhirayr Avetisyan and I created a math riddle about the games cops and robbers. It was part of an outreach event to high-school student at Ghent University. You can find it in this post here. The story was that a group of mathematicians wants to walk around the city of Ghent and have fun, while a group of bureaucrats wants to destroy that fun.
1. The New Version for SUSTech
This year I was asked to make a riddle for Pi Day at my new university, the Southern University of Science and Technology (SUSTech) in Shenzhen, China. Now I was asked very short notice, so I simply wanted to re-use last year’s riddle. There were two problems: (1) I can hardly use a city map of Ghent for a riddle at a university in Shenzhen. (2) In Belgium or Germany most civil servants and bureaucrats do not mind when people make fun of them. Indeed, I probably know all my civil servant jokes from civil servants (E.g.: Two civil servants meet in the hallway. One speak: “Oh! You cannot sleep either?”). Even though China is probably the most bureaucratic country which I have ever lived in (and I have lived in Germany, obviously), this is serious business and the story had to be replaced. The responsible secretary come up with a very cute story: A robot escaped from the robotics lab and students have to catch it again.
Here is the map of SUSTech’s campus:
Everyone moves in turns. A move is either staying put or moving to an adjacent place (indicated by a black line). I assume that the Chinese text says the same, but I am not the right person to ask for that? You can read it below.
The five best answers on WeChat got a prize. No answer was really good, but many got the right answer and some were decent.
The picture was in the press release for the event. It also made me get a haircut the next day.
2. My Old Solution
Actually, my old post just referred to the paper by Aigner and Fromme which (as far as I know) invented cops and robber games as a research topic. But last year I also made a few nice pictures for the solution:
The idea is very simple: You need three students/bureaucrats/cops $ {B_1, B_2, B_3}$ to catch the robot/mathematician/robber $ {B}$. Let $ {d(\cdot,\cdot)}$ denote the distance in the graph. Each $ {B_i}$ covers one of the possible exist. The pictures above show how the $ {B_i}$ can chase $ {M}$. You can work out the details (it is a riddle after all).
3. Chinese Regional Culture Festival
Two days later, I went to a regional culture festival on campus. It was organized by the student union if I understand it correctly. It was very nice for me as I do not know much about regional Chinese cuisine. Here you see some of the food which the students produced.
But why mention this? Towards the end of me trying all the food, I had the following conversation with a student. (Note: I am writing this three days later, so the dialog will not be fully accurate. Also, I made it more concise for readability.)
I wait at a stand for fish stew.
Me: Can I have some?
Stew serving student S: Yes, just wait two minutes. Where are you from?
Me: Germany.
S (excited): Wow! I have heard that German universities are very hard.
Me: I do not know.
S: Is that not why you are here?
Me: I work here.
S: Oh! Are you an English teacher?
Me: No, I am an assistant professor in mathematics.
Also waiting student B joins the conversation: You asked that Pi Day riddle!
Me: Yes, that is me.
B (excited): Oh! I tried to solve it. It was too hard!
A (suddenly unhappy): I also tried to solve it.
Me: Did you like it?
A (still unhappy): No. I could not solve it. Here, take your food.
Let us end with a picture of me there with my new haircut:
